A comparison of the antigenicity characteristics of mixed antigens in the child and the guinea-pig.

Parallel dose-response experiments were carried out in infants and guinea-pigs employing mixed antigens, e.g., diphtheria formoltoxoid (plain) mixed with H. pertussis vaccine, and with H. pertussis vaccine and tetanus toxoid (plain).It is found that the slopes of the dose-response regression lines, particularly in respect of the diphtheria antitoxin responses, are so greatly different in the two species that the guinea-pig cannot be used as a test-animal for response in children and that the concept of "units of antigenicity" receives no practical support.Since the adjuvant effect of pertussis vaccine on formol-toxoid appears to be inconstant, it is suggested that this property be regarded solely as a "bonus" to the intrinsic antigenic activity of the toxoid and that, for purposes of laboratory control of such mixed antigens, the toxoids should be tested against the International Toxoids (plain) alone, i.e., not mixed.